Genome complexity: new review of epigenetics studies (Introduction)

by David Turell , Wednesday, May 10, 2017, 19:57 (2753 days ago) @ David Turell

Have you ever constructed a shed or small building? I have several times. It requires planning the structure and then using materials you already have or getting new materials. This is how evolution makes a new species. Note these two articles which show the implied purpose behind the development of this jaw bone structure:

http://www.nature.com/nature/journal/v545/n7653/full/545158d.html?WT.ec_id=NATURE-20170...

"The tuatara of New Zealand (Sphenodon punctatus; pictured), formerly thought to be a lizard, was recognized 150 years ago this month as the only living member of its own reptile group — Rhynchocephalia (A. Günther Phil. Trans. R. Soc. 157, 595–629; 1867).

"The tuatara's ancestors separated from those of lizards and snakes (Squamata) around 240 million years ago. The frame-like skull of S. punctatus, long believed to be an archaic feature, is in fact a specialization for supporting its powerful jaws (D. I. Whiteside Phil. Trans. R. Soc. Lond. B 312, 379–430; 1986).

"The animal's taxonomic isolation has turned it into a flagship species for studies of evolution, biodiversity and conservation (see, for example, A. Cree Tuatara Canterbury Univ. Press; 2014)."

Abstract:

"The skull and lower jaw of a new sphenodontid reptile Diphydontosaurus avonis is described from disarticulated bones. The fossils were recovered from a detrital limestone of Rhaetian age deposited within solutional and tectonically formed fissures within the Carboniferous Limestone of Tytherington quarry near Bristol. The bone remains, numbering over 1000, are exquisitely preserved with intact facets. Diphydontosaurus was the smallest member of an insular fauna, was primarily insectivorous, and probably formed locally high-density populations. Uniquely for a sphenodontid, Diphydontosaurus had pleurodont teeth on the premaxilla and on the anterior regions of the dentary and maxilla. However, Diphydontosaurus also has the series of acrodont teeth alternating in size on the maxilla and dentary which is characteristic of the Sphenodontidae and particularly Sphenodon. An analysis of 49 synapomorphs in the Diapsida emphasises the sphenodontid nature of Diphydontosaurus. A study of these synapomorphs among the other Triassic sphenodontids Clevosaurus and Planocephalosaurus and the eosuchian Gephyrosaurus suggests that the lack of a quadrate-quadratojugal conch and the complete lower temporal bar are secondarily derived in the `living fossil' Sphenodon punctatus. The tuatara is therefore much less archaic than hitherto proposed. Functional reasons are advocated for the loss of the conch and the regrowth of a complete lower temporal bar. Transformation series are described which could have led to the shape of the maxilla, dentary, premaxilla, palatine and to the loss of the lacrimal in Sphenodon."

Comment: Of course there are 'functional reasons' for changes. They require planning. The big black box in our discussions is our lack of knowledge. We can tell which genes control what function or what appears in embryogenesis but we have no idea how the controls work, how the gene actually does its direction through chemical action. Until we have this knowledge, if it is possible to find, we will have no idea how speciation occurs. A fluffy nod to intelligence in cells tells us nothing of what we need to know. What is obvious is the need for prior planning, which only a competent mind can provide.